diff --git a/hosts/ocaml/browser/compile-modules.js b/hosts/ocaml/browser/compile-modules.js
new file mode 100644
index 00000000..c9c9dc21
--- /dev/null
+++ b/hosts/ocaml/browser/compile-modules.js
@@ -0,0 +1,128 @@
+#!/usr/bin/env node
+/**
+ * compile-modules.js — Pre-compile .sx files to bytecode JSON.
+ *
+ * Uses the js_of_ocaml kernel in Node.js to compile each .sx module,
+ * then serializes the bytecode as JSON for fast browser loading.
+ *
+ * Usage: node compile-modules.js [dist-dir]
+ */
+
+const fs = require('fs');
+const path = require('path');
+const crypto = require('crypto');
+
+const distDir = process.argv[2] || path.join(__dirname, 'dist');
+const sxDir = path.join(distDir, 'sx');
+
+if (!fs.existsSync(sxDir)) {
+  console.error('sx dir not found:', sxDir);
+  process.exit(1);
+}
+
+// Load the js_of_ocaml kernel
+const kernelPath = path.join(__dirname, '..', '_build', 'default', 'browser', 'sx_browser.bc.js');
+if (!fs.existsSync(kernelPath)) {
+  console.error('Kernel not found:', kernelPath);
+  process.exit(1);
+}
+require(kernelPath);
+const K = globalThis.SxKernel;
+if (!K) { console.error('SxKernel not initialized'); process.exit(1); }
+
+const FILES = [
+  'render.sx', 'core-signals.sx', 'signals.sx', 'deps.sx', 'router.sx',
+  'page-helpers.sx', 'freeze.sx', 'bytecode.sx', 'compiler.sx', 'vm.sx',
+  'dom.sx', 'browser.sx', 'adapter-html.sx', 'adapter-sx.sx', 'adapter-dom.sx',
+  'boot-helpers.sx', 'hypersx.sx', 'harness.sx', 'harness-reactive.sx',
+  'harness-web.sx', 'engine.sx', 'orchestration.sx', 'boot.sx',
+];
+
+// Load all files to build up the env (need compiler loaded)
+console.log('Loading SX environment...');
+for (const file of FILES) {
+  const r = K.load(fs.readFileSync(path.join(sxDir, file), 'utf8'));
+  if (typeof r === 'string' && r.startsWith('Error')) {
+    console.error('  FAIL', file, r);
+    process.exit(1);
+  }
+}
+console.log('  ' + FILES.length + ' files loaded');
+
+// Compile each file to bytecode
+console.log('Compiling bytecode modules...');
+let compiled = 0, skipped = 0;
+
+for (const file of FILES) {
+  const srcPath = path.join(sxDir, file);
+  const src = fs.readFileSync(srcPath, 'utf8');
+  const hash = crypto.createHash('sha256').update(src).digest('hex').slice(0, 16);
+
+  try {
+    // Parse source to get expression list, then compile
+    const code = K.eval('(compile-module (sx-parse ' + JSON.stringify(src) + '))');
+
+    if (typeof code === 'string' && code.startsWith('Error')) {
+      console.error('  SKIP', file, '—', code);
+      skipped++;
+      continue;
+    }
+
+    const json = {
+      magic: 'SXBC',
+      version: 1,
+      hash: hash,
+      module: serializeModule(code),
+    };
+
+    const outPath = srcPath.replace(/\.sx$/, '.sxbc.json');
+    fs.writeFileSync(outPath, JSON.stringify(json));
+    const size = fs.statSync(outPath).size;
+    console.log('  ok', file, '→', Math.round(size / 1024) + 'K');
+    compiled++;
+  } catch (e) {
+    console.error('  SKIP', file, '—', e.message || e);
+    skipped++;
+  }
+}
+
+console.log('Done:', compiled, 'compiled,', skipped, 'skipped');
+
+// --- Serialization ---
+
+function serializeModule(code) {
+  return {
+    bytecode: extractList(code.bytecode),
+    constants: extractList(code.constants).map(serializeConstant),
+  };
+}
+
+function extractList(v) {
+  if (!v) return [];
+  if (Array.isArray(v)) return v;
+  if (v._type === 'list' && v.items) return v.items;
+  if (v.items) return v.items;
+  return [];
+}
+
+function serializeConstant(c) {
+  if (c === null || c === undefined) return { t: 'nil' };
+  if (typeof c === 'number') return { t: 'n', v: c };
+  if (typeof c === 'string') return { t: 's', v: c };
+  if (typeof c === 'boolean') return { t: 'b', v: c };
+  if (c._type === 'symbol') return { t: 'sym', v: c.name };
+  if (c._type === 'keyword') return { t: 'kw', v: c.name };
+  if (c._type === 'list') return { t: 'list', v: extractList(c).map(serializeConstant) };
+  // Code object (nested lambda bytecode)
+  if (c.bytecode) return { t: 'code', v: serializeModule(c) };
+  if (c._type === 'dict') {
+    // Check if it's a code object stored as dict
+    const bc = c.get ? c.get('bytecode') : c.bytecode;
+    if (bc) return { t: 'code', v: serializeModule(c) };
+    // Regular dict
+    const entries = {};
+    if (c.forEach) c.forEach((v, k) => { entries[k] = serializeConstant(v); });
+    return { t: 'dict', v: entries };
+  }
+  return { t: 'nil' };
+}
diff --git a/hosts/ocaml/browser/sx_browser.ml b/hosts/ocaml/browser/sx_browser.ml
index e0a6e0e6..4f839628 100644
--- a/hosts/ocaml/browser/sx_browser.ml
+++ b/hosts/ocaml/browser/sx_browser.ml
@@ -231,6 +231,34 @@ let api_load src_js =
   | Eval_error msg -> Js.Unsafe.inject (Js.string ("Error: " ^ msg))
   | Parse_error msg -> Js.Unsafe.inject (Js.string ("Parse error: " ^ msg))
 
+let api_load_module module_js =
+  try
+    let code_val = js_to_value module_js in
+    let code = Sx_vm.code_from_value code_val in
+    let globals = Hashtbl.create 256 in
+    Hashtbl.iter (fun id v -> Hashtbl.replace globals (unintern id) v) global_env.bindings;
+    let _result = Sx_vm.execute_module code globals in
+    (* Copy all globals back into env — new defines + unchanged values *)
+    Hashtbl.iter (fun k v ->
+      Hashtbl.replace global_env.bindings (intern k) v
+    ) globals;
+    Js.Unsafe.inject (Hashtbl.length globals)
+  with
+  | Eval_error msg -> Js.Unsafe.inject (Js.string ("Error: " ^ msg))
+  | exn -> Js.Unsafe.inject (Js.string ("Error: " ^ Printexc.to_string exn))
+
+let api_compile_module src_js =
+  let src = Js.to_string src_js in
+  try
+    let exprs = Sx_parser.parse_all src in
+    let compile_fn = env_get global_env "compile-module" in
+    let code = Sx_ref.eval_expr (List [compile_fn; List exprs]) (Env global_env) in
+    return_via_side_channel (value_to_js code)
+  with
+  | Eval_error msg -> Js.Unsafe.inject (Js.string ("Error: " ^ msg))
+  | Parse_error msg -> Js.Unsafe.inject (Js.string ("Parse error: " ^ msg))
+  | Not_found -> Js.Unsafe.inject (Js.string "Error: compile-module not loaded")
+
 let api_render_to_html expr_js =
   let expr = js_to_value expr_js in
   let prev = !_sx_render_mode in
@@ -624,6 +652,8 @@ let () =
   Js.Unsafe.set sx (Js.string "evalExpr") (wrap api_eval_expr);
   Js.Unsafe.set sx (Js.string "renderToHtml") (Js.wrap_callback api_render_to_html);
   Js.Unsafe.set sx (Js.string "load") (Js.wrap_callback api_load);
+  Js.Unsafe.set sx (Js.string "loadModule") (Js.wrap_callback api_load_module);
+  Js.Unsafe.set sx (Js.string "compileModule") (wrap api_compile_module);
   Js.Unsafe.set sx (Js.string "typeOf") (Js.wrap_callback api_type_of);
   Js.Unsafe.set sx (Js.string "inspect") (Js.wrap_callback api_inspect);
   Js.Unsafe.set sx (Js.string "engine") (Js.wrap_callback api_engine);